Vacuum residues, yellowish-green to dark brown liquid to semi-solid/solid consisting of polyaromatic hydrocarbons along with metals and heteroatoms, are mainly heavy petroleum residues derived from crude oil in refineries on vacuum distillation at a condition of temperature more than 550° C. Processing of such residues is associated with very high energy intensive operations due to rapid poisoning of catalysts and thereby is termed as waste from refinery. Such waste materials are mostly used in the construction, paving/road making, and roofing. These residues have high carbon to hydrogen ratio and as such can be utilized for the synthesis of many carbonaceous materials like carbon wool, carbon fiber, graphene, needle coke, pet coke etc.
On the other hand, light olefins (C2-C4) are highly valuable base stock for the production of n-number of daily useful petrochemical products. C2-C4 olefins are traditionally produced by thermal or catalytic cracking of naphtha or gas or vacuum gas oil. Market demand of C3/C2 olefin is in rise of 10-20% per annum while that for C4/C2 is of 30-40% per annum. The key is that markets have become supply-driven and the shortage in supply has made the olefin market is of great profitability. The necessity for alternative production routes for these major commodity chemicals via non-oil-based processes has driven research in past times during the oil crises. Currently, there is a renewed interest in producing lower olefins from alternative feed stocks such as coal, natural gas, or biomass, in view of high oil price fluctuations, environmental regulations, and strategies to gain independence from oil imports. With the increasing demand of these olefins and diminishing resources of crude petroleum and upcoming of gas and availability of carbonaceous resources (biomass, coal etc.), it is very important to develop processes based on these alternative feed stocks. Partial oxidation to syngas followed by Fischer-Tropsch synthesis seems to be one of the most promising routes in current century other than the methods of catalytic cracking of naphtha and dehydrogenation of alkanes. However, the selectivity of the desired products ruled by the Anderson-Schulz-Flory (ASF) model has always restricted the application of this method to an industrial setting.
The processes of converting synthesis gas into light olefins can be divided into two categories i.e., indirect and direct. The indirect routes involve selective synthesis of methanol or dimethyl ether or FT wax from syngas followed by their conversion to light olefins in second step, while the direct process involves a single step which is considered to be cost effective in terms of equipment and energy consumption.
Reference may be made to Patent CN102926031, wherein a cost effective process for the synthesis of carbon fibers from petroleum pitch/heavy aromatic hydrocarbon feed/asphalt has been described.
Reference may be made to Patent CN102728328, wherein asphalt has been used for automobile exhaust gas absorber along with porous material such as carbon fiber, carbon black, activated carbon.
Reference may be made to Patent CN10320450, wherein a method is reported for the preparation of high specific surface area activated carbon from carbon-rich residue obtained from high temperature coal tar or coal tar pitch. The carbon-rich residue mainly comprises quinoline insolubles and toluene insolubles removed from high temperature coal tar or coal tar pitch. The method includes subjecting the carbon-rich residue to pre-oxidation, grinding, dipping, drying, carbonization, activation and other processes so as to prepare an activated carbon material with a high specific surface area and a large pore volume that can be used in environmental protection, food processing, fine chemicals, medicines, super capacitors and other fields.
Reference may be made to Patent EP2920344, wherein description of a method of making a carbon fiber has been mentioned using reduced Tg lignin with a carbon residue selected from the group of coal based raw material, petroleum based raw material and combinations thereof. Reference may be made to Patent application No. US20030077450, wherein a method for synthesizing carbonaceous porous material having excellent mechanical strength has been disclosed from carbon residue at 500° C. or higher temperatures.
Reference may be made to PCT Application No. WO201623041, wherein a method for the synthesis of graphenes from crude oil derived asphaltene or any other polyaromatic hydrocarbon feed has been disclosed.
Reference may be made to Patent JP2006248817, wherein a manufacturing method for carbon nanotube from low-cost heavy hydrocarbons by chemical vapor deposition at 800-1300° C. has been disclosed.
Reference can be made to the Patent CN100341777C, wherein a practical method for the synthesis of carbon microballs/fullerenes from heavy oil residuals has been disclosed at high temperature of about 1100° C. The microballs are equally of spherical shape and free of byproducts such as carbon fibers and graphite flakes.
Reference may be made to U.S. Pat. No. 4,460,454, wherein a process for producing a pitch from heavy oil residue has been disclosed. The pitch could be used to produce carbon fibers having desirable characteristics.
Reference may be made to U.S. Pat. No. 4,604,185, wherein a process for the up-gradation of vacuum residues to fuel ranges distillates has been disclosed by using a feed consisting of vacuum residue and cracked residuum.
Reference may be made to Patent CN102698754B, wherein a preparation method of iron loaded carbon sphere has been disclosed and the catalytic activity of these materials for degradation of organic pollutants has been described.
Reference may be made to Patent CN102151575B, wherein a preparation method of iron loaded carbon nanotube has been disclosed and the materials have been reported to show activity for hydrogenation/dehydrogenation reactions in liquid phase.
Reference may be made to Patent CN105057001, wherein synthesis of an iron loaded carbon nanotube catalyst for the direct coal liquefaction hydrogenation reactions has been disclosed.
Reference may be made to the Patent WO201069133, wherein a promising catalyst composition has been described consisting of activated carbon with other support material and having one or more active metal sites e.g., Cu, Zn, V, Cr, Mn, Fe, Co, Ni, Zr, Mo, Sn and La etc. for the conversion of syngas (H2:CO mostly greater than 2:1) to variety of chemicals like lower olefins up to the selectivity of 50%.
Reference may be made to Patent CN103394354B, wherein a preparation method for an iron loaded carbon sphere catalyst has been disclosed. The catalyst combinations shown to have syngas conversion activity with selectivity to methane 40 to 50% and lower olefins 35 to 40% at CO conversion of 50 to 80% at condition of temperature 340° C. and pressure 2.0 MPa at H2:CO mole ratio 2:1. The catalyst with the effective composition disclosed has been reported to be prepared by using ion exchange resin beads which were placed in an aqueous solution of iron precursor salt with or without combination of auxiliary agents for a sufficient ion exchange, adsorption, precipitation and/or dipping so as to be uniformly supported and distributed on the surface of the ion exchange resin/or bore. The resin then undergoes extensive washing to remove excess catalyst effective component and/or auxiliary agents or their precursors followed by drying to remove moisture. The catalyst then obtained by thermal decomposition of the exchanged resins under inert atmosphere.
Reference may be made to Patent CN103406137B, wherein the invention is related to a nitrogen-doped carbon nanotube supported catalyst for Fischer-Tropsch synthesis of lower olefins. The catalyst has reported to show activity for CO conversion up to 15% with selectivity up to 47% and 55% for lower olefins in absence and presence of alkali promoters respectively while the selectivity of methane is up to 23% and 17%. But, the selectivity for CO2 is 23% with alkali promoted catalyst while that without promoter is up to 18%.
Reference may be made to Patent CN102441384B, wherein a method for preparing iron loaded silica catalyst having high activity-stability carrier has been disclosed. The catalysts have shown to have activity in producing light olefins directly from syngas at condition of temperature up to 400° C., GHSV 1000 h−1, pressure 2.0 MPa and H2:CO (molar ratio) 1:1 in a high-pressure continuous fixed bed reactor with conversion of CO up to 80% and selectivity of light olefins (C2-C4) up to 50%. But no estimation on CO conversion to methane and CO2 has been reported. Herein, we report for the first time, a practical approach for the synthesis of iron incorporated sp2 carbon nanogranules from low value heavy petroleum residue/vacuum residue/polyaromatic hydrocarbons and the synthesized materials thereby provides an efficient catalyst system for direct synthesis of light olefin (C2-C4) from syngas with CO conversion up to 30% and lower olefin selectivity up to 50% at reduced methane and CO2 formation.